In this post, I thought i shall talk about coma and other altered states of awareness. What do we mean when we say a patient is in coma? Just what does coma mean?
Coma has been defined differently in different medical and neurology textbooks. In simple terms it means a patient who has decreased conciousness to the extent he is not aware of his surroundings and does not respond when stimulated by the external means even when the stimulus is noxious or painful like a pinch applied to the skin of the nipple. These patients are usually seriously ill and are in the intensive care unit of the hospital. As they are unaware of their external surroundings they need to be supported, meaning that their diet has to be maintained, their fluid status, making sure they are not constipated etc.
There can be numerous causes for coma. some of them are related to the brain itself and some of them are systemic, that is they affect the body.
1) Neurotrauma: head injuries frequently can lead to a coma with loss of consciousness sometimes for prolonged periods of time. Intracranial hemorrhage or bleeding into the brain is one cause of this. This bleeding raises the intracranial pressure and this compresses the brainstem and hence leads to coma.
2) Large stroke: a large stroke can lead to loss of consciousness and coma. Again a large stroke frequently leads to an increase in intracranial pressure and this leads to a depression in the state of awareness and coma.
3) Infections of the brain like meningitis and encephalitis may also lead to a state of coma.
4) Large tumors of the brain can also present with depression in sensorium (decreased consciousness) and coma.
5) Frequent seizures one after the other (this condition is referred to as status epilepticus): patients may be unresponsive even though they are not visibly “shaking” (that is there are no convulsive movements but patients are unresponsive because their brain is still having seizures).
6) Anoxic hypoxic injuries to the brain: anoxia is lack of blood flow and oxygen to the brain. This kind of coma is frequently irreversible.
7) Systemic causes of coma: metabolic conditions like low sodium (hyponatremia), low blood glucose (hypoglycemia), metabolic acidosis ( as seen in diabetic ketoacidosis), liver dysfunction (cirrhosis), renal dysfunction and renal failure, congestive heart failure, hypercapnia (where there is too much carbon dioxide in the blood) all are common causes of coma.
8) Toxins: ingestion of toxins like drugs of abuse, heavy metals, insecticides, overdose of antidepressants, pain killers, sedatives can all lead to coma.
As the causes of coma are protean, when patients present to the hospital in a comatosed state, we do a rapid triage and try to localize the etiology of the coma. Blood is drawn to check for sodium, potassium, liver and renal functions and glucose. If there is some evidence that an infectious etiology is the cause of coma we may draw blood for culture and do a spinal tap to examine the spinal fluid to rule out meningitis. Depending upon the history and examination findings other investigations may be carried out like CT scan brain, MRI brain, Chest X-ray, EEG and so on.
The treatment of “coma” depends upon the cause of coma. Frequently as I stated above these patients need to be admitted to the intensive care unit and need respiratory and circulatory support. Depending upon the cause of the coma, they may or may not need neurosurgical intervention. If there is a big bleed in the brain and the intracranial pressure is too high, the blood may need to be removed (evacuated). These patients may need broad spectrum antibiotic coverage if they have an infection or an antiepileptic drug if they are having seizures. If toxin or drug ingestion is the cause, then we try to remove the toxin or drug from the blood stream with the aid of an antidote.
Nitin Sethi, MD